Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay minerals.
As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand by mixing the oil sand with water and separating the sand from the aqueous phase of the slurry formed.
Disadvantages of such aqueous extraction processes are the need for extremely large quantities of process water (typically drawn from natural sources) and issues with removing the bitumen from the aqueous phase (whilst emulsions are being formed) and removing water from the bitumen-depleted sand.
Other methods have proposed non-aqueous extraction processes to reduce the need for large quantities of process water. An example of such a non-aqueous extraction process is disclosed in e.g. U.S. Pat. No. 3,475,318.
U.S. Pat. No. 3,475,318 discloses a process of removing bitumen from oil sands by solvent extraction with subsequent solvent recovery. After mixing the tar sands with a C5 to C6 hydrocarbon solvent in a dissolution zone whilst maintaining a solvent-to-bitumen weight ratio of from 0.5:1 to 1.5:1, the resultant mixture is passed to a classifier thereby obtaining an underflow of extracted sand. The extracted sand is passed through a counter-current extraction column and subsequently introduced in a first and second fluid-bed drying zone.
There is a continuous desire to improve the process efficiency in methods for extracting bitumen from an oil sand feed stream. It is an object of the present invention to meet this desire and to provide a more efficient method for extracting bitumen from an oil sand feed stream.
It is another object of the present invention to provide an alternative non-aqueous solvent based extraction process for extracting bitumen from an oil sand.
It is a further object of the present invention to efficiently separate solvent from the extracted sand.
It is an even further object of the present invention to provide a more efficient drying operation of the extracted sand, whilst reducing residual solvent levels in the sand to levels suitable for land reclamation.